Immunostimulation in crustaceans: does it really protect against infection?

Adaptive immunity in invertebrates: A straw house without a mechanistic foundation

“…The shellfish aquaculture industry is desperate to find ways to minimize the consequences of disease outbreaks, and is seeking to develop prophylactics to protect stock animals from infection. (33) Phenomenological observations of 'priming', functional adaptivity or 'memory' continue to provide the 'scientific basis' to support the aquaculture pharmaceutical industry. (58)(59)(60) Numerous products are now marketed globally as additives to enhance the immunity of commercially cultured species, mainly shrimp.…”

“…As the shellfish farming industry continues to grow, successful treatments that acquire good 'credibility' are set to become 'big earners' for the manufacturers. As previously reviewed (33) however, all mechanistic studies so far have failed to support the conclusion that any stimulation of the invertebrate immune system is sufficiently long-lived to constitute a proper solution to the problem of recurrent disease within the context of invertebrate aquaculture. The limits of immune stimulation as a strategy have only been realized with the advent of detailed studies of cellular, protein and molecular processes, questioning the reliance on phenomena in isolation as a means of advancing or exploiting our knowledge of invertebrate innate immune systems.…”

“…They bind to molecules within the host immune system, the pattern recognition receptors (PRRs), to form a complex that then initiates a series of events, such as signal transduction or activation of enzyme cascades that result in the liberation of bioactive molecules. What actually happens when protostome invertebrates are injected with PAMPs is that a full-blown immune response occurs, involving activation of particular enzyme cascades, such as the prophenoloxidase system, the regulated exocytosis of aggressive molecules, (4,13) an increase in the expression of genes coding for antimicrobial proteins (17,20,23) and /or other related proteins (see Table 1 and Smith et al (33) ), and the initiation of encapsulation reactions leading to haemocytopenia. Experiments in which presentation of PAMPs to the protostome immune system has been claimed to 'prime' the immune system, measure not immune parameters, as might be expected, but survival, (5) temporary increases in growth (34,35) or reproductive capacity.…”

“…In the case of a successful immune response, the released and activated components will persist within the haemocoel until broken down by the host or, in the case of degranulated haemocytes, are replaced by recruitment of haemocytes to the site of infection (17) and haemopoiesis. (37) In decapod crustaceans, mechanistic evidence of this temporal signature has definitively been shown to last between 3 and 72 hours (reviewed by Smith et al; (33) see also Table 1). Thus any effect on the immune system is short-lived and the 'cost' to the host is potentially high.…”

Hsp70 expression in shrimp Litopenaeus vannamei in response to IHHNV and WSSV infection

“…During the past 20 years, viral diseases have been among the main causes of economic looses in shrimp farming, particularly in Asia and South America [2]. Factors contributing to the spread of diseases pre-selection of stocks of animals for growth rather than disease resistance, intensive farming practices that favor the transmission of pathogens and immunosuppressive effect by high densities and stress transport [20]. Invertebrates rely on innate immunity to respond to the entry of foreign microorganisms [7].…”